Space-based radar and communications system designs arc generally limited by power-aperture product for transmissions and by the antenna aperture for receptions. In both types of systems the beamwidth becomes narrower as the aperture becomes larger, forcing the beam to be scanned if larger coverage is desired, as it often is. Reflector type antennas are notoriously limited in the scan angle that they can attain, to about 10 to at most 20 beamwidths before beam distortion and growth in sidelobes becomes so large as to render performance unacceptable. Phased array antennas do not suffer the same limitations, but are in general much more complex, heavy, and expensive than the same aperture reflector antennas due to the number of components and the strict positional requirements of the elements for their functioning. This is especially true for space based radar systems that detect, identify and track targets near the Earth's surface, that require large antenna apertures together with fine sidelobe control while attaining large beam scan angles which are needed in order to achieve adequate signal-to-noise ratio and clutter rejection to perform moving target detection.
Thus, it would be desirable to be able to provide very large space antennas that are free of the limited scan angle of reflector or array-fed reflector antennas, yet are much lighter and less complex than pure electronically steerable antennas. By way of example, it would be desirable to be able to implement antennas with aperture in the tens to hundreds of meters while simultaneously having aerial densities of less than 1 kg/square meter and yet be able to scan their beams dozens if not hundreds of beamwidths. In addition it would be very desirable to simplify the feeds of such antennas and their associated data processing units to both reduce weight, cost, and complexity and increase reliability. The resulting reduction in power, processing, complexity and weight requirements would, in turn, provide for a significantly lighter and less expensive spacecraft and for a smaller launcher, without compromising space system performance. This application describes novel means to implement such antennas, regardless of their application.